This application is based on and claims priority to Japanese Patent Application No. 2000-390256, filed Dec. 22, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates generally to an air induction system for an internal combustion engine, and more particularly to an improved and compact air induction system that is tuned to enhance engine performance at both low and high speeds.
2. Description of the Related Art
An internal combustion engine typically includes an air induction system through which air is introduced into one or more combustion chambers of the engine. The induction system typically includes an intake silencer and one or more intake conduits. The silencer coordinates or smooths the air flow and reduces induction system noise. The conduits communicate air from the silencer to the combustion chambers.
The length of the intake conduits play an important role in determining the torque characteristics of the engine. Generally, relatively long intake conduits improve engine torque at low and/or middle engine speeds, and relatively short intake conduits are desired to improve engine torque at high engine speeds.
Efforts have been made to provide an engine air induction system having both long and short intake conduits so as to improve engine torque characteristics in both low and high engine speed ranges. Such induction systems typically include extra parts and require more space than traditional systems. An especially difficult problem arises when an engine must be placed within a strictly confined space. For example, a typical outboard motor includes an engine surrounded by a protective cowling. Space for the intake conduits and air induction system is extremely limited, and enlarging the cowling to make a roomier space is not an acceptable option because outboard motors are required to be as compact as possible for carriage and storage.
The preferred embodiments of the present invention provide an outboard motor engine air induction system which can be tuned to improve engine torque characteristics at both low/medium engine speeds and high engine speeds without significantly increasing the space required by the induction system.
In accordance with one aspect, the present invention comprises an outboard motor comprising a power head having a cowling enclosing a space. An engine is disposed within the cowling and is configured to drive a substantially vertically oriented crankshaft, and. An air induction system is also disposed within the cowling and is configured to deliver air from the space into a combustion chamber of the engine. The air induction system comprises an intake silencer and at least one intake runner. The intake silencer has an outer wall, an inlet port through the wall for drawing air from the space into the intake silencer, and a runner extension pipe integrally formed with the intake silencer. The runner extension pipe has an upstream end and a downstream end. The upstream end opens within the intake silencer and the downstream end opens into the intake runner. A runner hole is formed through the outer wall of the intake silencer and communicates with the intake runner at a point adjacent the downstream end of the runner extension pipe. A valve is disposed in the outer hole and is configured to selectively open and close the hole. When the valve is closed, an intake passage is defined from the upstream end of the runner extension pipe to a downstream end of the runner pipe. When the valve is opened, the intake passage is defined from the runner hole to the downstream end of the runner pipe.
In accordance with another aspect, the intake silencer additionally comprises a dividing wall dividing the silencer into a first chamber and a second chamber. At least one connection passage is formed through the dividing wall, and a dividing wall valve within the connection passage selectively closes the passage.
In accordance with yet another aspect of the present invention, an air induction system is provided for improving the torque characteristics of an outboard marine engine. The air induction system is also configured to be positioned within a limited space between the engine and an associated protective cowling. The induction system comprises an intake silencer and an intake manifold. The intake manifold has at least one generally linear runner extending from the silencer to the engine. The runner opens into the silencer at a runner opening. A runner opening valve is disposed in the runner opening and is configured to selectively close the opening. A runner extension has an upstream end opening into the silencer and a downstream end opening into the runner so that an intake passage between the silencer and the engine is effectively lengthened when the runner opening valve is closed.
In accordance with a further aspect, an air induction system is provided for improving the torque characteristics of an engine. The induction system comprises an intake silencer and an intake manifold, the intake manifold comprising at least one generally linear runner extending from the silencer to the engine. The runner opens into the silencer at a runner opening. A runner opening valve is disposed in the runner opening and is configured to selectively close the opening. A runner extension is provided and has an upstream end opening into the silencer and a downstream end opening into the runner.
In accordance with a still further aspect, a method of improving torque characteristics of an outboard motor engine at low, middle and high engine speeds is provided. An intake silencer and an intake conduit are provided. The intake conduit extends from the intake silencer to an intake passage of the engine. A second intake conduit extends from the intake silencer to a portion of the first intake conduit. The method includes automatically closing a valve between the silencer and the first intake conduit during low and medium engine speeds so as to provide a long flow path extending from the silencer through the second intake conduit and first intake conduit to the intake passage of the engine. The method further includes automatically opening the valve between the silencer and the first intake conduit during high engine speeds so as to provide a shortened flow path extending from the silencer through the first intake conduit to the intake passage of the engine.
In accordance with a further aspect of the above method, the intake silencer comprises two chambers separated by a dividing wall, and a balancing passage is formed through the wall. A balancing valve is positioned in the balancing passage. The method additionally includes closing the balancing valve at low speeds so that each chamber functions as a separate intake silencer, and opening the balancing valve at high speeds so that the effective volume of the intake silencer comprises the collective volume of the two chambers.